In general, after a stack of a fuel cell is assembled and manufactured, since activity of the stack of the fuel cell in an electrochemical reaction is low upon initial driving, a process known as stack activation is performed to maximally secure normal initial performance of the stack of the fuel cell. An object of activation of the fuel cell known as pre-conditioning or break-in is to activate catalyst that is not involved in a reaction and to sufficiently hydrogenate an electrolyte membrane and electrolyte contained in an electrode to secure a hydrogen ion passage. More particularly, to exhibit performance of a normal state after the stack of the fuel cell is assembled, the stack activation process is performed with the object of securing an electrode reaction area of three-phases, removing impurities from a polymer electrolyte membrane or the electrode, and improving ion conductivity of the polymer electrolyte membrane.
In a method for activating a stack according to the related art described above, a pulse discharge configured in a high current density discharge and a shutdown state is performed repeatedly, and a process time is about 1.5 to 2 hours based on a 220 cell submodule. More particularly, the method for activating a stack according to the related art is performed by repeatedly performing a process in which high current density (e.g., 1.2 or 1.4 A/cm2) is discharged for 3 minutes, and a process in which the pulse discharge is performed for 5 minutes in the shutdown state about 11 times.
However, in the activation process according to the related art using the above-mentioned pulse discharge, an amount of used hydrogen as well as a processing time is increased. In other words, the existing method for activating a stack using the pulse discharge in the shutdown state has an advantage that activation speed is increased by changing an internal water flow of the fuel cell. However, since the time required for the activation is about 105 minutes and an amount of used hydrogen is about 2.9 kilograms based on the 220 cell submodule, the processing time is increased and a consumption amount of hydrogen is increased.